The mechanical pump comprises a pump rotor with radially slidable vanes rotating within a shiftable control ring, whereby the control ring is pushed by a plunger pushing the control ring into high pumping volume direction. The plunger is shiftably arranged in a control chamber. The pump comprises a pressure control system to control the discharge pressure of the pressurized lubricant leaving the pump. The pump's discharge pressure is controlled by controlling the position of the shiftable control ring by controlling the pressure in the hydraulic control chamber, thereby moving the plunger.
Variable displacement vane pumps of the state of the art have previously been described in WO 2005/026553 A1. The pump is provided with a pressure control system to control the discharge pressure of the lubricant. The pressure control system comprises a first pressure control chamber wherein a first plunger is provided which is axially movable. The first pressure control chamber is connected via a pressure conduit with the pump outlet port. The pressure control system also comprises a separate control element which is realized as a cylinder-piston-element which keeps the pressure of the pressurized lubricant provided by the pump at a more or less constant level, independent of the rotational speed of the pump rotor. This is realized by opening and closing a control outlet of the first pressure control chamber, thereby moving the control ring into a low pumping volume direction or pushing the control ring into a high pumping volume direction.
The lubricant pressure requirement is, however, dependent on the working conditions of the engine, such as the lubricant temperature. The lubricant pressure requirement is lower at high lubricant temperatures and higher at low lubricant temperatures.